1. Field of the Invention
The present invention relates to an electric power system protection and control system in combination of digital protection controllers, such as digital relays, to protect and control an electric power system by inputting status quantities of the electric power system and converting them into digital data and a display controller to display and control the monitoring of operation and status of the digital protection controllers via a communication network, and a distributed control system.
2. Description of the Related Art
Digital protection controllers, such as digital relays, are already used widely in the field of the electric power system, and are made highly functional by use of highly efficient microprocessors and memories of large capacity, etc. in recent years. In particular, for the power saving of their operation and maintenance, it becomes possible to realize a remote operation and monitoring system for operating and monitoring the operation and status of digital protection controllers via a wide area transmission network from a long distance.
In these systems, it is possible to display electrical quantities (current and voltage quantities converted into digital data) input from an electric power system at a distant place via a transmission system in addition to the detailed information relative to the operation and status of digital protection controllers. Definite examples of these systems are disclosed in literatures, for instance, (The 1996 National Meeting of The Institute of Electrical Engineers of Japan, Lectured Theses 1529 "Development of Digital Relay Remote Operation Monitoring System").
On a system for the purpose of the remote operation of conventional digital protection controllers, such as digital relays, it takes such a form that along the remote operation menu of digital protection controllers (hereinafter referred to as "Protection Controllers"), a request is submitted from a remote personal computer via a wide area transmission network. When this request is received, the protection controller performs the process according to the request and returns a response to the personal computer that sent the request. An example of the remote operation menu is shown in FIG. 18.
A case is taken to change the setting, for example, the setting of a threshold value of the relay operation in a digital relay, according to a setting menu as an example. As shown in FIG. 19, the steps will be as shown below: First, selecting a display control menu after selecting a substation and equipment and connecting the communication according to a communication menu within a remote operation menu; and then, after further selecting the setting, setting elements to be changed are selected, numerical values to be changed are input and a writing request is submitted to EEPROMs in the protection controller, and thereafter, an operation starting request is submitted.
In this case, until a series of processings is completed, it is necessary to maintain the connection between the personal computer and the protection controllers. Accordingly, there will be a first problem that delay of communication accompanied with increase in the traffic on a communication network and drop of reliability generated from loss of communication packets.
FIG. 19 shows the change of one setting element. But so as to change plural setting elements, a required time further increases. Further, to have a personal computer generate various requests corresponding to the above-described remote operation menu, it is required for the operator to operate the personal computer to each request.
This means that when functions of a protection controller become complicated and versatiled, the number of operations increase and workload of the operator increases. Further, when plural protection controllers are required to execute the same operation, it becomes complicated as the same work is performed for different controllers, and there will be caused such a second problem that with the increase of workload, the drop of reliability due to human error will be generated.
Further, in case of such a remote operation system, plural protection controllers are operated by a single personal computer. In this case, it will become necessary to configure the system by taking differences in the substances of protection controllers (for instance, setting elements due to different protection relaying scheme) into consideration.
The configuration in this case is shown in FIG. 20. As shown in this FIG. 20, the configuration at the personal computer side is corresponding to the kinds of protection controllers. This means that with the increase in kinds of protection controllers, the volume of the corresponding software that is to be provided on a personal computer increases, and there will be such a third problem that the necessity for modification is produced and the economy and reliability of the system will become worse.
Further, in such a remote operation system, as a local network and a wide area transmission network are used, the protection controllers can be easily operated remotely at a place where they can be connected to these communication networks. In other words, the remote operation can be made similarly through personal computers installed at plural locations.
This state is shown in FIG. 21. In this case, it is necessary to provide a remote operation software that is corresponding to each protection controller to each personal computer as described above, and there will be a fourth problem that this system is inferior in the aspect of economy such as required expenses and maintenance.
Further, as it becomes possible to monitor the operation of plural protection controllers by a single personal computer in the remote operation system as described above, it is possible to compare related same items (for instance, electrical quantities of the system taken by plural protection controllers connected to the same system).
In this case, a personal computer is connected to protection controllers subject for communication and displays operating items along the remote operation menu shown in FIG. 18. If it is desired to check the state of the same items on other related controllers, a personal computer is connected similarly to the related controllers for communication and displays the items along the operation menu shown in FIG. 18.
In this case, if the number of protection controllers subject for control is increased, such operations as selection of controllers, connection for communication and selection of items become necessary for each protection controller and the operations becomes very complicated, and related other protection controllers and items are displayed independently for each protection controller. However, as they are not displayed as related protection controllers and items in the same picture, there will be such a fifth problem that the comparison of related items will become an overload for operator.
In this case, it is considered to consolidate the menu for every same related items over plural controllers. But if it is required to see different items for each controller, it will be complicated conversely, and in addition, the maintainability will become a problem when there is an increase/modification of the controller. Further, there will be such a sixth problem that if the same protection controller is accessed simultaneously by plural display controllers, the processing load of the protection controller increases in order to respond to the access and therefore, a response is delayed.
Further, for such a remote operation system there is the possibility for demand to realize versatile functions. For instance, conventionally the protection, control and measurement of an electric power system are separated as separate controller. It is considered to consolidate these functions in the same controller. In this case, there will be a seventh problem that the processes to be incorporated in a protection controller increase and an excessive load is generated in the aspect of the economical efficiency, reliability and maintainability.
Further, when changing the specification of a protection controller, it is a general practice to stop the controller and change a ROM containing a program, and there will be an eighth problem that the drop of availability of the system and complicated changed workload.